Static Electricity Chapter 7
Static Charges In this chapter we will learn: • Atoms with equal negative and positive charges are called neutral • Atoms can become charged when electrons transfer in or out of a material • Insulators do not allow electric charges to move easily • Conductor is a material in which electric charges can move more easily • The unit for measuring charge is the coulomb.
Static Charges • When you think of the word “electricity” you think of computers, televisions and other modern devices. • The earliest studies of electricity had to do with static charges which refers to electric charges that can be collected and held in one place.
Static Charges • Can you think of some instances when you have been affected by static charges? • Clothes coming out of a dryer • Rubbing your feet on the carpet • Touching a lock with a key and seeing a spark • Lightening is when a static charge builds up in the ground during a thunderstorm.
Early Theories of Electricity • Benjamin Franklin discovered a type of “electrical fluid” in certain objects when they were rubbed. He called a build up of this fluid positive (+) and a shortage negative (-). Scientists still use these symbols to show the movement of electrical energy.
Positive and Negative Charge in Atoms • All matter is made of atoms - at their centre is a nucleus containing protons (positively charged) and neutrons (no charge). Surrounding the nucleus are electrons (negatively charged). • Solid materials are charged due to the movement of electrons - when electrons are gained, the object becomes negative. When electrons are lost, the object becomes positive.
Friction and Electron Transfer • Electrons are most often transferred through friction, when objects rub against each other. • Friction results in losing electrons or gaining electrons.
Insulators and Conductors • Materials that do not allow charges to move easily are called electrical insulators. • Some good INSULATORS are: • plastic • ceramics • wood • glass Only insulators are good at retaining static charge.
Insulators and Conductors • Materials that allow electrons to travel freely are called electrical conductors. • Some good conductors are: • metals (ex. copper, zinc, cadmium)
Measuring Charge • Unit of electric charge is called a Coulomb (C) , named after the French physicist Charles Augusin de Coulomb. • 1 C of charge is equal to the removal or addition of 6.25 x 1018 electrons. • A typical lightening bolt carries 5 – 25 C
Generating Static Charge A Van de Graaff generatoruses friction to produce a large static charge on a metal dome. The moving belt produces a static charge at the base and this is carried to the top of the dome where it is collected.
Applications of Static Electricity • Plasticsandwich wrap clings due to static charges. • Static devices are used in industry to remove pollutants from chimney stacks. • Air ionizers in homes. • Static charges are used in painting automobiles.
Dangers of Static Electricity • When static charge builds up it can discharge and cause serious shocks, explosions or fires. • Those pumping flammables must ensure objectsare grounded (connected to the Earth sothat static charge is discharged). • Lightning is especially dangerous - buildingscan be protected with lightning rods.
7.2 Electric Force • Force is a push or pull - electric force can doboth, without touching the object - it is anaction-at-a-distance force. Laws of Static Charge • Like charges repel • Opposite charges attract • Neutral objects areattracted to chargedobjects
Charging Objects Charging By Conduction • Charging through direct contact • Extra electrons will move to a locationwhere there is less of them
Charging Objects Charging By Induction • Bringing a charged object nearby aneutral object will cause chargemovement and separation in thein the neutral object. Section 7.2 Quiz